U.S. patent application number 16/516292 was filed with the patent office on 2019-11-28 for stirred bead grinding mills.
The applicant listed for this patent is OUTOTEC (FINLAND) OY, SWISS TOWER MILLS MINERALS AG. Invention is credited to Jeff BELKE, Alex Heath, Edward Allan Jamieson.
Application Number | 20190358638 16/516292 |
Document ID | / |
Family ID | 62978896 |
Filed Date | 2019-11-28 |
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United States Patent
Application |
20190358638 |
Kind Code |
A1 |
BELKE; Jeff ; et
al. |
November 28, 2019 |
STIRRED BEAD GRINDING MILLS
Abstract
A stirred bead grinding mill includes a substantially
cylindrical grinding shell and a central stirring shaft within the
grinding shell. The central stirring shaft is provided with axially
spaced stirring elements, preferably grinding discs, along the
central stirring shaft. A replaceable grinding element is provided
that includes an axial support structure arranged to form the outer
periphery of the grinding element adapted to fit within the
grinding shell, and at least one counter disc arranged to project
radially inward from the axial support structure to an extent
separating two grinding zones in an axial direction while allowing
the central stirring shaft within the grinding shell, wherein at
least part of the counter disc and/or the support structure is
provided with castellations.
Inventors: |
BELKE; Jeff; (West Perth,
AU) ; Heath; Alex; (Leeming Perth, AU) ;
Jamieson; Edward Allan; (Bayswater, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OUTOTEC (FINLAND) OY
SWISS TOWER MILLS MINERALS AG |
Espoo
Baden |
|
FI
CH |
|
|
Family ID: |
62978896 |
Appl. No.: |
16/516292 |
Filed: |
July 19, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/FI2017/050042 |
Jan 26, 2017 |
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16516292 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B02C 17/16 20130101;
B02C 17/22 20130101; B02C 17/18 20130101 |
International
Class: |
B02C 17/16 20060101
B02C017/16; B02C 17/22 20060101 B02C017/22 |
Claims
1.-44. (canceled)
45. A grinding element for a stirred bead grinding mill used in
grinding mineral ore particles having a preferably cylindrical
grinding shell and a central stirring shaft within the grinding
shell, wherein the grinding element comprises: an axial support
structure arranged to form the outer periphery of the grinding
element adapted to fit within the grinding shell, and at least one
counter disc arranged to project radially inward from the axial
support structure to an extent separating two grinding zones in an
axial direction while allowing the central stirring shaft within
the grinding shell, wherein at least part of the counter disc
and/or the support structure is provided with castellation.
46. The grinding element of claim 45, wherein the grinding element
has a cross-section of a hollow cylinder or an arc segment of a
hollow cylinder, preferably a cross-section of an arc segment in a
range from 20 degrees to 180 degrees of a hollow cylinder, more
preferably a cross-section of a hollow half-cylinder.
47. The grinding element of claim 45, wherein the grinding element
is dimensioned to be installed side by side with one or more
further grinding elements in a radial plane within the grinding
shell to form a grinding element assembly with a cross-section of a
hollow cylinder.
48. The grinding element of claim 45, wherein the grinding element
has an axial length that is smaller than the axial length of the
cylindrical grinding shell, preferably an axial length that is
smaller than the axial length of the grinding shell.
49. The grinding element of claim 45, wherein the grinding element
is dimensioned to be stacked up with one or more further grinding
elements in the axial direction within the cylindrical grinding
shell to form a grinding element assembly having a desired total
axial length.
50. The grinding element of claim 45, wherein the central stirring
shaft is provided with axially spaced stirring elements, preferably
grinding discs, along the central stirring shaft, and wherein at
least one counter disc is arranged to project radially inward from
the axial support structure at an axial location which is offset
from axial locations of stirring elements of the stirring
shaft.
51. The grinding element of claim 45, wherein the axial support
structure comprises an axial sidewall defining an outer peripheral
surface of the grinding element, and wherein the at least one
counter disc is arranged to project radially inward from an inner
surface of the axial side wall.
52. The grinding element of claim 51, wherein the axial support
structure further comprises a plurality of spaced wear-protective
elements provided along an inner surface of the axial sidewall of
the support structure and protruding inwardly from said inner
surface a plurality of wear protective elements provided on the
inner surface of the axial sidewall to protrude radially inwards
from the inner surface of the sidewall.
53. The grinding element of claim 45, wherein the grinding element
has a cage-like structure in which the axial support structure
comprises a plurality of elongated spaced support members defining
the outer periphery of the grinding element, and the at least one
counter disc is connected to and arranged to project radially
inward from the plurality of elongated spaced support members of
the axial support structure.
54. The grinding element of claim 52, wherein the plurality of the
protective elements or the plurality of elongated spaced support
members is arranged to form a skeleton for lining with a dissimilar
material, which lining is arranged to be sacrificed during the
grinding operation in order to expose the protective elements or
the elongated spaced support members, respectively.
55. The grinding element of claim 45, wherein the grinding element
is a stand-alone element adapted for a loose fit mounting within a
grinding shell.
56. The grinding element of claim 45, wherein the grinding element
is connectable to one or more further grinding elements to form a
larger stand-alone grinding element assembly adapted for a loose
fit mounting within a grinding shell.
57. A grinding element assembly comprising grinding elements
according to claim 45.
58. A stirred bead grinding mill comprising a substantially
cylindrical grinding shell and a central stirring shaft within the
grinding shell, and at least one grinding element of claim 45.
59. A method of using the grinding element of claim 45, comprising
utilizing the grinding element in mineral ore grinding.
60. A method of using the grinding element of claim 45, comprising
utilizing a grinding media having a diameter selectable from a
range of approximately 0.5-20 mm depending on a F80 of the
particulate material and a P80 of the ground particulate material
in each specific grinding application.
61. A method of refurbishing the grinding element of claim 45,
comprising: removing the grinding element from a stirred bead
grinding mill, and replacing or rebuilding a worn castellation of
the grinding element.
62. The method of claim 61, wherein the rebuilding comprises
building the castellation back up to replace worn material.
63. The method of claim 61, wherein the rebuilding comprises
building the castellation back up to replace worn material using
one or more of following techniques: depositive welding, 3D
printing, addition of rubber or polymer to the worn areas.
64. The method of claim 61, wherein the replacing comprises
attaching new castellation to the grinding element by one or more
of bolting, riveting, welding, gluing, and cementing.
Description
FIELD OF THE INVENTION
[0001] The invention relates to improvements in stirred bead
grinding mills for grinding mineral ore particles.
BACKGROUND OF THE INVENTION
[0002] Stirred bead grinding mills are typically used in mineral
processing to grind mineral ore particles into smaller sized
particles to facilitate further downstream processing, such as
separation of the valuable mineral particles from unwanted gangue.
For example, mineral ore particles in the range of about 30 .mu.m
to 4000 .mu.m in diameter may be ground down to particles of 5 to
100 .mu.m in diameter.
[0003] A stirred bead grinding mill typically has a stationary mill
body or shell arranged vertically in the mill and an internal drive
shaft. The drive shaft has a plurality of stirring elements, such
as grinding discs or rotors, so that rotation of the drive shaft
also rotates the stirring elements, which in turn stirs a suitable
grinding media, and the mineral ore particles, in the form of a
feed slurry, passes through this stirred bed of media. The
resulting stirring action causes the mineral ore particles to be
ground into smaller sized particles. However, the grinding discs
and the shell tend to suffer from high wear, especially when the
grinding mill is operated at high speeds through the action of the
harder grinding media acting against the grinding discs.
BRIEF DESCRIPTION OF THE INVENTION
[0004] An aspect of the invention is a grinding element for a
stirred bead grinding mill used in grinding mineral ore particles
having a preferably cylindrical grinding shell and a central
stirring shaft within the grinding shell, wherein the grinding
element comprises
[0005] an axial support structure arranged to form the outer
periphery of the grinding element adapted to fit within the
grinding shell, and
[0006] at least one counter disc arranged to project radially
inward from the axial support structure to an extent separating two
grinding zones in an axial direction while allowing the central
stirring shaft within the grinding shell, wherein at least part of
the counter disc and/or the support structure is provided with
castellations.
[0007] In an embodiment, the grinding element has a cross-section
of a hollow cylinder or an arc segment of a hollow cylinder,
preferably a cross-section of an arc segment in a range from 20
degrees to 180 degrees of a hollow cylinder, more preferably a
cross-section of a hollow half-cylinder.
[0008] In an embodiment, the grinding element is dimensioned to be
installed side by side with one or more further grinding elements
in a radial plane within the grinding shell to form a grinding
element assembly with a cross-section of a hollow cylinder.
[0009] In an embodiment, the grinding element has an axial length
that is smaller than the axial length of the cylindrical grinding
shell, preferably an axial length that is smaller than the axial
length of the grinding shell.
[0010] In an embodiment, the grinding element is dimensioned to be
stacked up with one or more further grinding elements in the axial
direction within the cylindrical grinding shell to form a grinding
element assembly having a desired total axial length.
[0011] In an embodiment, the central stirring shaft is provided
with axially spaced stirring elements, preferably grinding discs,
along the central stirring shaft, and at least one counter disc is
arranged to project radially inward from the axial support
structure at an axial location which is offset from axial locations
of stirring elements of the stir-ring shaft.
[0012] In an embodiment, the axial support structure comprises an
axial sidewall defining an outer peripheral surface of the grinding
element, and wherein the at least one counter disc is arranged to
project radially inward from an inner surface of the axial side
wall.
[0013] In an embodiment, the axial support structure further
comprises a plurality of spaced wear-protective elements provided
along an inner surface of the axial sidewall of the support
structure and protruding inwardly from said inner surface a
plurality of wear protective elements provided on the inner surface
of the axial sidewall to protrude radially inwards from the inner
surface of the sidewall.
[0014] In an embodiment, at least part of the protective elements
comprises elongated protective elements extending parallel or
almost parallel with along the inner surface of the axial sidewall
of the axial support structure.
[0015] In an embodiment, at least part of the elongated protective
elements comprise two or more protective element segments cascaded
in line or in other pattern.
[0016] In an embodiment, the axial profile and/or side profile of
the protective elements comprises at least one or more of a
block-shaped element, a vane, and a fin.
[0017] In an embodiment, the plurality of the protective elements
is arranged to form a skeleton for lining with a dissimilar
material, which lining is arranged to be sacrificed during the
grinding operation in order to expose the protective elements.
[0018] In an embodiment, the grinding element has a cage-like
structure in which the axial support structure comprises a
plurality of elongated spaced support members defining the outer
periphery of the grinding element, and the at least one counter
disc is connected to and arranged to project radially inward from
the plurality of elongated spaced support members of the axial
support structure.
[0019] In an embodiment, at least part of the plurality of
elongated spaced support members is arranged to extend parallel or
almost parallel with the axial direction, and/or inclined relative
to the axial direction and/or non-linearly relative to the axial
direction.
[0020] In an embodiment, at least part of the plurality of
elongated spaced support members comprise curved support beams.
[0021] In an embodiment, the plurality of elongated spaced support
members is arranged to form a skeleton for lining with a dissimilar
material, which lining is arranged to be sacrificed during the
grinding operation in order to expose the elongated spaced sup-port
members.
[0022] In an embodiment, the at least one counter disc comprises
castellation on one side of the counter disc.
[0023] In an embodiment, the at least one counter disc comprises on
both sides of the counter disc.
[0024] In an embodiment, the at least one counter disc comprises
castellation on an inner radial edge of the counter disc.
[0025] In an embodiment, the castellation comprises spaced members
at intervals of 10-60 degrees in a tangential direction, preferably
at intervals of 10-45 degrees, more preferably at intervals of
10-30 degrees, even more preferably at intervals of 10-20
degrees.
[0026] In an embodiment, a height of the castellation in the axial
direction is in a range from 0.5 to 3 times an axial thickness of
the counter disc, preferably about the same as the thickness of the
counter disc.
[0027] In an embodiment, a height of the castellation is within
range of 2 mm to 200 mm, preferably within range of 5 mm to 150 mm,
more preferably within 10 mm to 100 mm.
[0028] In an embodiment, a ratio of a height of the castellation to
the spacing of the castellation is within range of 1/2 to 1/20,
preferably within range of 1/5 to 1/20, more preferably within
range of 1/8 to 1/12.
[0029] In an embodiment, a width of the castellation in a
tangential direction is from 1 mm to about a thick-ness of the
counter disc, preferably from 5 mm to about the thickness of the
counter disc, more preferably about the thickness of the counter
disc.
[0030] In an embodiment, a total width of all castellation in a
tangential direction is less than 0.25 to 0.35 times a tangential
length of the grinding element.
[0031] In an embodiment, an orientation of the castellation is
within range of 0 degrees to 90 degrees, preferably within range of
0 degrees to 25 degrees, more preferably within 0 degrees to 10
degrees of inclination relative to the radial direction of the
counter disc.
[0032] In an embodiment, the castellation extends across the
counter disc from the axial support structure to a radially inner
edge of the counter disc.
[0033] In an embodiment, the castellation extends across a portion
of the counter disc between the axial support structure to a
radially inner edge of the counter disc, preferably across the
inner portion of counter disc close to the inner edge of the
counter disc.
[0034] In an embodiment, the castellation extends beyond a radially
inner edge of counter disc, preferably around the inner edge to
join to a castellation on the opposite side of the counter
disc.
[0035] In an embodiment, the castellation is only on a radially
inner edge of the counter disc.
[0036] In an embodiment, the grinding element is a stand-alone
element adapted for a loose fit mounting within a grinding
shell.
[0037] In an embodiment, the grinding element is connectable to one
or more further grinding elements to form a larger stand-alone
grinding element assembly adapted for a loose fit mounting within a
grinding shell.
[0038] In an embodiment, the grinding element is configured to be
used with a grinding media having diameter selectable from a range
of approximately 0.5-20 mm depending on a F80 of the particulate
material and a P80 of the ground particulate material in each
specific grinding application.
[0039] In an embodiment, the grinding element is a refurbished
grinding element.
[0040] Another aspect of the invention is a grinding element
assembly comprising grinding elements according to any one of
embodiments above.
[0041] A further aspect of the invention is a stirred bead grinding
mill comprising a substantially cylindrical grinding shell and a
central stirring shaft within the grinding shell, and at least one
grinding element of any one of embodiments above.
[0042] In an embodiment, the central stirring shaft is provided
with axially spaced stirring elements, preferably grinding discs,
along the central stirring shaft.
[0043] In an embodiment, the stirred bead grinding mill comprises a
vertical or horizontal disc mill.
[0044] Still another aspect of the invention is use of the grinding
element of any one of embodiments above in mineral ore
grinding.
[0045] Another aspect of the invention is use of the grinding
element of any one of embodiments above with a grinding media
having diameter selectable from a range of approximately 0.5-20 mm
depending on a F80 of the particulate material and a P80 of the
ground particulate material in each specific grinding
application.
[0046] A further aspect of the invention is a method of
refurbishing the grinding element of any one of embodiments above,
comprising
[0047] removing the grinding element from a stirred bead grinding
mill, and
[0048] replacing or rebuilding a worn castellation of the grinding
element.
[0049] In an embodiment, the rebuilding comprises building the
castellation back up to replace worn material.
[0050] In an embodiment, the rebuilding comprises building the
castellation back up to replace worn material using one or more of
following techniques: depositive welding, 3D printing, addition of
rubber or polymer to the worn areas.
[0051] In an embodiment, the replacing comprises attaching new
castellation to the grinding element by one or more of bolting,
riveting, welding, gluing, and cementing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] In the following the invention will be described in greater
detail by means of exemplary embodiments with reference to the
attached drawings, in which
[0053] FIG. 1 is a perspective view of an exemplary grinding mill
suitable for comprising grinding elements according to an
embodiment of the invention;
[0054] FIG. 2 is a side view of the grinding mill of FIG. 1;
[0055] FIG. 3 is a front view of the grinding mill of FIG. 1;
[0056] FIG. 4 is a cross-sectional side view of a portion of an
exemplary mill body used in the grinding mill of FIG. 1;
[0057] FIG. 5A is a perspective view of an exemplary flat grinding
disc;
[0058] FIG. 5B is a perspective view of an exemplary counter
disc;
[0059] FIG. 6 is a perspective view of an exemplary castellated
grinding disc;
[0060] FIG. 7 is an elevation view of an exemplary castellated
grinding element on a counter disc.
[0061] FIG. 8 is a perspective view of an exemplary castellated
grinding element having a cross-section of a hollow
half-cylinder;
[0062] FIGS. 9A-9H show cross-sectional side views of different
exemplary grinding elements.
[0063] FIGS. 10A-10C show perspective views of exemplary
castellated grinding elements having different types of
cross-sections;
[0064] FIGS. 11A-11B show perspective views illustrating stacking
of exemplary castellated grinding elements;
[0065] FIGS. 12A and 12B illustrate an exemplary installation of
grinding elements according to exemplary embodiments into a
grinding mill;
[0066] FIG. 13 is a side view of an exemplary grinding element
having a cage-like structure; and
[0067] FIG. 14 is a cross-sectional side view of castellation
elements embedded in a coating of a dissimilar sacrificial
material.
EXEMPLARY EMBODIMENTS OF THE INVENTION
[0068] The present invention will now be described with reference
to the following examples which should be considered in all
respects as illustrative and nonrestrictive.
[0069] It will also be appreciated that embodiments of the
invention are readily applicable to various types of mineral ore
having a variety of particle sizes and particle size distributions.
Particle size of the feed and discharge are typically measured.
Hence, the particle size of the slurry (e.g. the particulate
material and a slurrying liquid) at the feed inlet is typically
described by its F80, meaning that 80% of the feed particles (by
mass) pass through a nominated screen mesh size. For example, an
F80=1000 .mu.m means that 80% of the total mass of particles
present will pass through a 1000 .mu.m screen aperture. An
alternative size description is F100, meaning that 100% of the feed
particles pass through a nominated screen mesh size. Similarly, it
will be understood by one skilled in the art that P80 means that
80% of the mass of discharged particles pass through a nominated
screen mesh size. For example, a P80=60 .mu.m means that 80% of the
mass of particles present in the discharge will pass through a 60
.mu.m screen aperture. Embodiments of the invention have been
primarily developed to process particle sizes in the range of
F80=30 .mu.m to F80=4000 .mu.m, especially in the range of F80=80
.mu.m to F80=1000 .mu.m for the incoming particulate material and
particles sizes in the range of P80=0.1 .mu.m to P80=800 .mu.m,
especially in the range of P80=1 .mu.m to P80=400 .mu.m for the
ground discharged product. Hence, embodiments of the present
invention permit the grinding mill 1 to process a wide range of
particle sizes for mineral particles having a wider particle size
distribution in the above stated F80 and P80 ranges to produce very
fine particle sizes down to P80=1 .mu.m. Thus, embodiments of the
invention are readily applicable to many different types of
particulate materials and are not limited to particular mineral ore
types, but can include iron, quartz, copper, nickel, zinc, lead,
gold, silver and platinum. Other particulate materials that can be
processed using embodiments of the invention include concrete,
cement, recyclable materials (such as glass, ceramics, electronics
and metals), food, paint pigment, abrasives and pharmaceutical
substances. In these other applications, embodiments of the
invention are used to reduce the size of the particulate material
using a grinding process.
[0070] It will also be appreciated that embodiments of the
invention are readily applicable to various types of stirred bead
grinding mills having a stationary grinding shell and a central
stirring shaft with axially spaced stirring elements, preferably
grinding discs, provided along the shaft. Examples of suitable
stirred grinding mills are described in the applicant's co-pending
PCT patent application PCT/FI2016/050545 which is incorporated by
reference herein. In the following, examples of a structure and
operation of suitable stirred grinding mills, particularly disc
mills, are illustrated in order to make it easier to comprehend
embodiments of the invention, while the intention is not to
restrict the application of the invention to these exemplary
grinding mills.
[0071] In the Figures, corresponding features within the same
embodiment or common to different embodiments have been given the
same reference numerals. Referring to FIGS. 1 to 5, a stirred bead
grinding mill 1 for grinding a slurry having particulate material
may comprise a mill body 2 and a drive mechanism 4 for providing a
stirring action in the mill body 2 by rotating the drive shaft 11
of the mill body 2 about a longitudinal axis 6. The mill body 2 and
the drive mechanism 4 may be mounted on a frame structure, such as
on a base frame 3 and a drive frame 5, respectively, in the
illustrated exemplary embodiments. In the illustrated example the
mill body 2 may comprise a mounting assembly 9 for fitting the mill
body to the base frame 3 and operatively aligning the mill body to
the drive mechanism 4. In embodiments, the grinding mill may be a
fine grinding mill, and is called a high intensity grinding mill,
in which the rotating action results in intense grinding of the
slurry particles by the grinding media. Grinding mills may have a
relatively high power consumption in order to achieve fine
grinding, e.g. in the range from 5 kWhr/t to 100 kWhr/t (kilowatt
hours per tonne). The power intensity, kW/m.sup.3, of the grinding
mills may also be relatively high, e.g. up to 100-300 kW/m.sup.3,
or more.
[0072] A charge of feed slurry comprising mineral ore particles may
be fed into the mill body 2 through the bottom inlet 7 that is
shown as a centred inlet in this example. The mill body 2 may be
partially filled (e.g. about 2/3 filled) with grinding media, such
as small beads. Grinding media may also be added into the mill body
2 initially through the outlet 8, or via a separate entry into the
top of the mill, before the feed slurry (e.g. the particulate
material and a slurrying liquid) is added and the grinding mill 1
is put into operation. In operation, the mill body 2 or a stirring
mechanism 10 inside the mill body 2 is rotated by the drive
mechanism 4 about the axis 6 to rotate or stir the feed slurry and
grinding media together, thereby providing relative motion of the
slurry of grinding media and particulate material at a desired
speed within the grinding chamber and causing the feed slurry
particles to be crushed or ground against and between the grinding
media, whereby comminution takes place by attrition between the
grinding media. The tip speed of the stirring mechanism may be from
the range of 4-12 m/s, for example. The ground product may then be
discharged through the top outlet 8. The grinding media may
typically comprise ceramic or steel beads that range from 0.5 mm to
20 mm in diameter. The size of the grinding media may vary in other
embodiments, depending on requirements. For example, the diameter
of the grinding media can be 30 or 50 times the diameter of the
slurry particles, which can be measured by reference to F80 or
F100. For example, the grinding media diameter may be selected from
a range of approximately 0.5-20 mm depending on a F80 of the
particulate material and the P80 of the ground particulate material
in each specific grinding application, preferably from a range of
0.5-1.5 mm for F80 of 70 .mu.m or less and for P80 of 20 .mu.m or
less, preferably from a range of 1-3 mm for F80 of 50-100 .mu.m and
for P80 of 20-60 .mu.m, preferably from a range of 3-6 mm for F80
of 100-300 .mu.m and for P80 of 50-100 .mu.m and preferably from a
range of 6-20 mm for F80 of 300-4000 .mu.m and for P80 of 80-300
.mu.m.
[0073] Referring to FIG. 4, in the illustrated exemplary
embodiments, the shell 18 is arranged vertically in the grinding
mill and has a bottom inlet 7 and a top outlet 8. It will be
appreciated that in other embodiments, the mill body 2 may be
arranged to be inclined or at an angle in the grinding mill 1. In
some embodiments, the shell 18 may be arranged to lie horizontally
in the grinding mill. Likewise, in other embodiments, the inlet 7
and outlet 8 can be placed at locations of the shell other than the
bottom and top, respectively.
[0074] Referring to FIG. 4, an exemplary embodiment is illustrated
wherein the mill body 2 may comprise a generally cylindrical drum
or shell 18 that defines an internal cavity or grinding chamber 15,
and a rotating stirring device assembly 10 positioned within the
shell 18. The term "cylindrical" as used herein shall be understood
to refer generally to any cylinder-like structure with circular or
round cross-section. Although in the illustrated exemplary
embodiments the mill body may have generally cylindrical shape, it
will be appreciated that the mill body or the shell 18 can take
other cross-sectional shapes in other embodiments, such as
rectangular, square, oval or oval-like, or any other regular or
irregular polygonal shape, such as the hexagonal, defining the
grinding chamber 15. The stirring device assembly may comprise a
one or more drive shafts 11 to each of which may be mounted a
plurality of stirring devices 12 described in more detail below.
The one or more drive shafts may be coaxial with the mill body 2
(e.g. as illustrated in the exemplary embodiments), or not. The one
or more drives shafts may be parallel to a longitudinal axis 6 of
the mill body 2, as illustrated in the exemplary embodiments, or
the drive shaft may be inclined or at an angle to the axis of the
mill body. The stirring devices 12 may be coaxial with the axis of
the drive shaft, as illustrated in the exemplary embodiments, or
they may be non-coaxial. In the exemplary embodiments, the stirring
effect is caused by the rotating stirring devices 12 mounted on the
shaft 11. The stirring device assembly 10 takes the form of an
impeller or a rotor but is also known as a drive shaft assembly. As
such, the stirring device assembly will hereinafter be referred to
as a mill rotor in reference to this embodiment.
[0075] In embodiments, the stirring devices 12 in the mill rotor 10
may comprise a plurality of coaxial or non-coaxial grinding discs
12 spaced up the length of the drive shaft 11. An example of a
grinding disc 12 is illustrated in FIG. 5A. In the exemplary
embodiment, a grinding disc 12 may comprise a flat disc body 20
that may be connected via arms 22 (typically known as spokes) to a
mounting ring 21 for mounting the grinding disc 12 to the drive
shaft 11 of the stirring device assembly 10. Although in the
exemplary embodiment the stirring device is an annular disc, but it
will be appreciated that the stirring device can take other planar
forms in other embodiments, such as rectangular, square, oval or
oval-like, circular and any other regular or irregular polygonal
shape. It will be appreciated by one skilled in the art that for
industrial duties the annular disc size may range from 400 mm
diameter to 2500 mm diameter. However, the invention applies
equally to fine grinding discs of any size. Also, the stirring
devices 12 can have surfaces other than two opposed surfaces, such
as any number of surfaces that have the same or different shapes.
For example, the stirring devices may have an inclined or angled
surface, a curved surface, a corrugated surface, a saw-toothed
surface, irregular surface or any other regular or irregular shape.
In embodiments, grinding disc may have through holes, openings,
interruptions or cut outs. For ease of reference, the stirring
devices 12 in this embodiment will hereinafter be referred to as
grinding discs. However, embodiments of the invention are not
limited to any specific structure or design of a stirring device
assembly or stirring devices. For example, a stirring assembly may
alternatively comprise radial posts spaced up along a drive shaft.
As a further example, a stirring assembly may comprise a screw
auger.
[0076] There may also be a plurality of stationary planar annular
shelves or counter discs 14 on an internal side wall 13 of the mill
shell 18 positioned in between each rotational stirring device or
grinding disc 12. An example of a counter disc 14 is illustrated in
FIG. 5B. The planar annular shelves or counter discs 14 may extend
or protrude into the chamber 15 between the stirring devices or
grinding disc 12. The shelves 14 tend to subdivide the internal
chamber 15 into individual subchambers 17 interconnected through
openings 16 defined between the shelves 14 and the drive shaft 11.
Depending on the application, there can be any number of sets of
stirring devices 12 and shelves 14, such as the rotating and
stationary discs. For example, there may be up to several dozens of
sets, but typically 5-20.
[0077] In operation, the drive mechanism 4 rotates the drive shaft
11 of the stirring device assembly 10, rotating the grinding discs
12 that in turn provide rotational motion of the slurry of the
grinding media and the particulate material (as illustrated by the
transverse arrows in the Figures) at a desired speed within the
grinding chamber 15 of the mill body 2. The rotational motion
causes the feed slurry particles to be ground against and between
the harder grinding media, thus releasing valuable mineral
particles and reducing them in size for further downstream
processing after being discharged through the outlet 8. The slurry
flow transfers upwardly 17 through the opening 16 to the subchamber
17, passes through the rotating disc 12, then through the next
opening 16 to the next subchamber 17. The free space in each
subchamber 17 around the rotational grinding disc 12 can be
regarded as a classification stage where coarser particles move
towards the internal wall of the shell 18 while finer particles
move faster upwards through the openings 16. Due to the vertical
arrangement of the mill, classification is conducted simultaneously
throughout the grinding process with larger particles remaining
longer at the peripheral, while smaller particles move upwards.
[0078] In other words, in the exemplary vertical stirred bead mill
the feed slurry is fed from below, with the ore particles being
progressively ground smaller by the moving grinding media beads
before exiting from the top of the grinding mill. The grinding
media beads are significantly larger (e.g. tens of times larger)
than the ore particles, which is necessary for grinding, and also
keeps the grinding media beads inside the grinding mill due to
their ability to settle faster than the upward flow rate of the
feed slurry. The mill may be, however, sized such that the grinding
media beads are partially fluidised by the upward flowing feed
slurry. The electric power draw to drive the shaft is sensitive to
the feed flow rate, i.e. at higher flow rates the grinding media
beads are lifted slightly and exert less resistance on the grinding
discs. In a horizontal stirred bead mill, a centrifugal separator
may be provided at the end of the mill to keep the beads and
coarser particles in the mill.
[0079] In stirred media mills, the shear forces are significant.
Ideally the grinding mill would not wear, but in practice liner and
disc wear are inevitable even in well designed and built equipment.
Accelerated wear of the components of the grinding mill makes their
operational life very short, thus requiring more frequent
replacement than desired. The frequent replacement of the grinding
mill components also increases the amount of downtime, reducing the
efficiency of the grinding mill, as well as increasing maintenance
costs.
[0080] Uneven wear of the grinding discs has been observed in
stirred grinding mills, with the wear occurring faster for the
lower grinding discs (at the feed end) than for the upper grinding
discs (at the discharge end). Preferably the grinding discs would
last a number of months, and wear more evenly so that they would be
due for replacement at the same time. One cause of the uneven wear
may be that the grinding media beads are only partially fluidized,
meaning that only a portion of their weight is carried by the
upward flow of feed slurry. The remainder of the gravitational
force is born downwards through the packed bed of grinding media
beads such that the gravitational force is highest at the bottom of
the grinding mill. This increases the force on the mill shell, and
also the grinding discs, which are then subject to a higher wear
rate towards the bottom of the grinding mill. Another cause of the
uneven wear may be that the coarse feed particles are introduced
into the bottom of the grinding mill, which is likely to also
increase the wear rate at the base of the grinding mill. Similar
uneven wear occurs also in horizontal stirred grinding mills which
also wear faster at the feed end.
[0081] In the applicant's co-pending PCT patent application
PCT/FI2016/050545, which is incorporated by reference herein,
embodiments are proposed in which a protective castellation may be
provided on the stirring devices or grinding disc 12 to capture and
form a media layer against the rotating disc to minimize
differential speed between and media and disc, thereby reducing
wear. An exemplary embodiment of a grinding disc 12 provided with a
castellation 25 is illustrated in FIG. 6. In the exemplary
embodiment, the castellation may comprise protective elements 25
that may be provided adjacent to the outer edge of the disc body 20
to extend outwardly from the disc body 20. In an exemplary
embodiment, a mounting hub 21 may be connected via arms 22
(typically known as spokes) to the disc body 20 for mounting each
grinding disc 12 to the drive shaft 11 of the stirring device
assembly 11. The protective elements 25 in this embodiment take the
form of blocks or block-like elements that may be integrally formed
with the disc body 20 and arranged so that opposed sides and one
end of the blocks may project outwardly from the planar surfaces
and outer edge of the disc body 20. Each block 25 may thus extend
both substantially orthogonally relative to the opposed planar
surfaces via its opposed sides and radially outwardly from the
outer edge via its end. Alternatively, the protective elements 25
may be in the form of U-shaped blocks mounted to the disc body 20
so that opposed sides and one end of each block 25 extends or
projects outwardly from the planar surfaces and outer edge of the
disc body, respectively. It will be appreciated that the protective
elements 25 can take any number of forms in order to create the
zone around each grinding disc 12. Examples of other forms or
shapes of the protective elements are disclosed in the applicant's
co-pending PCT patent application PCT/FI2016/050545, which is
incorporated by reference herein.
[0082] In the applicant's co-pending PCT patent application
PCT/FI2016/050545, which is incorporated by reference herein,
embodiments are proposed in which a protective castellation 25 may
be provided on the shelves 14 to further minimise wear of the
shelves and the inner sidewalls, as illustrated in FIG. 7.
[0083] In spite of these improvements, there is still need for
reducing wear of the components of the grinding mills, reducing the
time and work required for replacement of components, reducing the
downtime, and/or reducing maintenance costs.
[0084] According to an aspect of the invention, a novel grinding
element for a stirred grinding mill is provided. The grinding
element comprises an axial support structure arranged to form the
outer periphery of the grinding element adapted to fit within a
grinding shell. The grinding element further comprises at least one
counter disc arranged to project radially inward from the axial
support structure to an extent separating two grinding zones in an
axial direction of the grinding shell while allowing the central
stirring shaft to be provided within the grinding shell. At least
part of the counter disc and/or the support structure is provided
with castellation.
[0085] In embodiments, the grinding element may have a
cross-section of any arc segment of a hollow cylinder, preferably a
cross-section of an arc segment in a range from 20 degrees to 180
degrees of a hollow cylinder, more preferably a cross-section of a
hollow half-cylinder.
[0086] An exemplary grinding element 80 having a cross-section of a
hollow half-cylinder is illustrated in FIG. 8. In the illustrated
example, the grinding element 80 comprises an axial support
structure in form of an axial sidewall 81 defining an outer
peripheral surface of the grinding element 80. The outer peripheral
surface of the grinding element 80 may be arranged to tightly or
loosely fit against the inner surface of the shell to form a
replaceable protective subshell or a liner which prevents the
actual shell 18 from wearing. The grinding element 80 further
comprises an annular counter disc 14 arranged to project radially
inward from an inner surface of the axial side wall 81. In
embodiments the counter disc 14 is arranged to project radially
inward from the axial support structure at an axial location which
is offset from axial locations of the grinding discs 12 of the
stirring shaft within the grinding shell 18.
[0087] In the exemplary grinding element 80 shown in FIG. 8, both
the axial sidewall 81 and the counter disc 14 are provided with
castellation 25A and 25A, respectively. A cross-sectional side view
of the grinding element 81 is illustrated in FIG. 9A. The
castellation 25A and 25B reduces wear of the sidewall 80 and the
counter disc 14, thereby prolonging the lifetime of the grinding
element 80. Further Examples of grinding elements 80 having
castellation 25A and 25B on both the axial sidewall 81 and on the
counter disc 14 are illustrated in FIGS. 9A, 9C, and 9D.
[0088] In embodiments there may be castellation 25A on the sidewall
81 only, as illustrate by an example in FIG. 9H.
[0089] In further embodiments there may be castellation 25B on the
counter disc 14 only, as illustrate by examples in FIGS. 9B, 9E,
9F, and 9G.
[0090] The castellation of the axial sidewall 81 may comprise a
plurality of spaced wear-protective elements 25A provided on the
inner surface of the axial sidewall 81 to protrude radially inwards
from the inner surface of the sidewall 81.
[0091] The protective elements 25A may be elongated protective
elements extending parallel with the axis of the grinding
element.
[0092] The counter disc 14 may comprise castellation on one or both
sides of the counter disc 14, as illustrated by examples in FIGS.
8, 9A, 9B, 9C, 9E, 9F, and 9G. In some embodiments there may be
castellation 25B on one or both sides of the counter disc 14 but
not on the inner radial edge of the counter disc 14, as illustrated
by examples in FIGS. 8, 9A, 9B, 9C, and 9E. In some embodiments
there may be castellation 25B on one or both sides of the counter
disc 14 and also on the inner radial edge of the counter disc 14,
as illustrated by examples in FIGS. 9D, 9F, and 9G.
[0093] In embodiments, the shelves or counter discs 14 may have
holes, interruptions or cut outs in order to enhance sludge
circulation.
[0094] In embodiments the castellation 25B may extend across the
radial width of the counter disc 14 from the inner sidewall 81 to a
radially inner edge of the counter disc 14, as illustrated in FIGS.
9A and 9B.
[0095] In some embodiments the castellation 25B may extend on one
side or both sides of the counter disc 14 on a portion of the
radial width of the counter disc, as illustrated in FIGS. 9C, 9D,
9F, and 9G, preferably across the inner portion of counter disc 14
close to the inner edge of the counter disc. In some embodiments
there may be castellation 25B on the inner radial edge of the
counter disc 14 or at the tip of the counter disc as illustrated in
FIG. 9D. In some embodiments, the castellation 25B may extend
beyond a radially inner edge of counter disc 14, preferably around
the inner edge to join to a castellation 25B on the opposite side
of the counter disc 14.
[0096] An exemplary grinding element 80 having a cross-section of a
hollow 1/3-cylinder (a 120 degrees segment of a cylinder) is
illustrated in FIG. 10A.
[0097] An exemplary grinding element 80 having a cross-section of a
hollow 1/4-cylinder (a 90 degrees segment of a cylinder) is
illustrated in FIG. 10B.
[0098] An exemplary grinding element 80 having a cross-section of a
hollow full-cylinder (360 degrees) is illustrated in FIG. 10C. In
this case a radius of the central opening 16 of the grinding
element 80 must be larger than an outer radius of a grinding disc
12 in order to allow a stirring shaft 11 and grinding discs 12 pass
through the opening 16 during installation.
[0099] In embodiments in which the grinding element may have a
cross-section of an arc segment of a hollow cylinder, a grinding
element 80 is dimensioned to be installed side by side with one or
more further grinding elements 80 in a radial plane within the
grinding shell 18 to form a grinding element assembly with a
cross-section of a hollow cylinder. For example, a pair of grinding
elements 80 having a cross-section of a half-cylinder (180 degree
segment) may be installed side by side to obtain a full hollow
cylinder, similar to that illustrated in FIG. 10C. Similarly three
grinding elements of 120 degrees, or four grinding elements of 90
degrees may side by side to form a grinding element assembly with a
cross-section of a hollow cylinder. In embodiments, the grinding
element 80 may comprise means for connection to one or more further
grinding elements. For example, such connection means may include
one or more of a clamp, a flange, a bolt connection. In
embodiments, the grinding element 80 may be a stand-alone element
adapted for a loose fit mounting within a grinding shell 18.
[0100] In embodiments, a grinding element 80 has an axial length
that is approximately equal to or a multiple of the distance
between the axially spaced grinding discs 12 of the central
stirring shaft 11. Generally, the grinding element has an axial
length that is smaller than the axial length of the cylindrical
grinding shell.
[0101] In embodiments, the grinding element 80 is dimensioned to be
stacked up with one or more further grinding elements 80 in the
axial direction within the cylindrical grinding shell 18 to form a
grinding element assembly 800 having a desired total axial length.
In an example illustrated in FIGS. 11A and 11B, four half-cylinder
grinding elements 80 are stacked on top of each other to form a
longer grinding element assembly 800. Similarly, the exemplary
grinding elements 80 shown in FIGS. 10A, 10A, and 10C, or other
type of grinding elements, can be stacked.
[0102] In embodiments, a grinding element assembly 800 may be
assembled or manufactured prior to installing the grinding element
assembly within the shell 18 of the grinding mill. In embodiments,
two or more grinding element assemblies 800 may be first formed,
and the grinding element assemblies 800 may then be installed and
stacked with a grinding shell 18 of the grinding mill.
[0103] In embodiments, a single grinding element 80 may comprise
two or more counter discs 14 in the axial direction. Such a single
grinding element having multiple counter discs may be manufactured
in various alternative ways, such as welding or casting. For
example, a single grinding element 80 having four counter discs 14
in the axial direction may be similar to the grinding element
assembly 800 shown in FIG. 11B.
[0104] In embodiments, the grinding element assembly 800 is a
stand-alone element adapted for a loose fit mounting within a
grinding shell 18.
[0105] FIGS. 12A and 12B illustrate an exemplary installation of
grinding elements 80 according to exemplary embodiments into a
grinding mill 1, more specifically within a grinding mill shell 18
of a grinding mill body. In the illustrated example, the, the mill
body 2 can be axially (e.g. vertically on a vertical mill and
horizontally on a horizontal mill) split down the centre into two
halves, or into three or more segments that can be moved apart. For
example, the two halves of the mill body may be flanged axially
(vertically) so that the can be separated. For example, the two
halves of the mil body 2 may be hinged together, so that upon
taking out flange bolts or like, the shell halves can be swung
apart. After exposing the internals of the shell 18, the
half-cylinder grinding elements 80 can be installed or mounted to
the two halves of the mill body 2 within the shell 18. Also the
grinding discs 12 can now be readily change, if desired. In the
illustrated example, nine half-cylinder grinding elements 80 are
stacked within each half of the mill body 2. Thereby, a
half-cylinder grinding element assembly 800 is provided within each
half of the mill body 2. The outer wall 81 of the grinding element
80 may be arranged to tightly or loosely fit against the inner
surface of the shell to form a replaceable protective subshell
which prevents the actual shell 18 from wearing. The grinding
elements 80 or the grinding element 800 may be connected to the
shell 18 by appropriate connecting means or they may be drop-in
units. The halves of the mill body 2 containing the grinding
elements 80 or grinding element assemblies 800 can now be connected
together around the stirring shaft 11 and the grinding discs 12 to
form a cylindrical drum 2 containing a subshell in a form of a
cylindrical grinding element assembly. The actual shell 18 is fully
protected from wearing. Worn grinding elements 80 can be easily
replaced by a reverse procedure: the mill body 2 is separated into
halves, the worn grinding elements 80 are selectively replaced, and
the mill body is reassembled. In case of uneven wear of the
grinding elements 80, individual worn grinding elements 80 can be
replaced and unworn elements 80 can be left unchanged, which
reduces the maintenance work and cost as well as spare part costs.
As practically only the grinding elements 80 will wear, the
lifetime of the mill body will be significantly prolonged.
[0106] As the castellation 25A and/or 25B on the grinding elements
80 typically wear out before the side wall 81 and the counter disc
14, it is possible to reuse a worn grinding element 80 by restoring
the castellation 25A and/or 25B. The new castellation 25A and/or
25B can be provided by various means, including a 3D printing, for
example. Alternatively the worn elements may be refurbished by
welding to build up the worn areas (steel liners), replacement of
worn castellation and/or counter discs by bolting/welding/riveting
etc. Polymer liners could be built up by the addition of new
polymer. Alternatively, worn areas may be repaired by attachment
harder materials like ceramic or carbide tiles by gluing,
cementing, bolting or any other means of attachment.
[0107] In the exemplary embodiments of the invention, the
castellation is implemented by block shaped elements which is the
preferred form. The castellation is not limited to the block-shaped
elements but the castellation may be implemented by any form of
projection that extends from the surfaces of the counter disc 14 or
the sidewall 81. In embodiments, the axial profile and/or side
profile of the castellation may comprise at least one or more of a
projection, an elongated body, a block-shaped element, a flange, a
tooth, a planar element, a vane, a blade, a fin, a plate, a bar, a
post, a rod, a channel-shaped element, a V-shaped element, a
U-shaped element, a ramp-like element and a wedge-shaped element.
Yet another embodiment has angled or inclined annular shelves 14
instead of being orthogonal to the sidewall 81.
[0108] In embodiments, the castellation may be dimensioned to
protrude from the sidewall and/or the counter disc 14 at a height
that is at least one half of a size of the grinding media,
preferably at least one and one half the size of the grinding
media, more preferably at least 3 times the size of the grinding
media. In embodiments, an inward height of the of the castellation
may be within range of 2 mm to 200 mm, preferably within range of 5
mm to 150 mm depending on the size of mill or disc, more preferably
within 10-100 mm.
[0109] The elements of the castellation may be spaced apart each
other in the circumferential direction, or in in a direction of the
rotational motion of the slurry of the grinding media and the
particulate material. In embodiments, the spaced castellation
elements are at intervals a of 10-60 degrees in a direction of the
rotational motion of the slurry of the grinding media and the
particulate material, preferably at intervals of 10-45 degrees,
more preferably at intervals of 10-30 degrees, even more preferably
at intervals of 10-20 degrees. In embodiments, a ratio of height of
the cancellation elements to the spacing between the neighbouring
castellation elements may be within range of 1/2 to 1/20,
preferably within range of 1/5 to 1/20, more preferably within
range of 1/8 to 1/12.
[0110] In embodiment, the castellation elements 25A may comprise
elongated castellation elements extending longitudinally between
the shelves or counter discs 14 on the sidewall 81 of the grinding
element 80. Longitudinally means that the elongated protective
elements may extend in direction which is transverse or at an angle
to the rotational motion of the slurry of the grinding media and
the particulate material, or parallel or at an angle to the axial
direction 6 of the mill body.
[0111] In an embodiment the elongated castellation elements 25A may
extend longitudinally between the shelves or counter discs 14 on
the sidewall 81 approximately parallel with the axis of the mill
shell 18.
[0112] In a further embodiment the elongated castellation elements
25A may extend longitudinally on the sidewall 81 of the grinding
element 80 approximately parallel with the axis of the mill shell
18.
[0113] In a vertical grinding mill the castellation elements 25A
may be vertical elements, and respectively, in a horizontal
grinding mill horizontal elements.
[0114] In embodiments, the elongated castellation elements 25A
extending longitudinally between the shelves or counter discs 14 on
the sidewall 81 of the grinding element 80 may be inclined or at an
angle to the axial direction 6 of the mill shell 18.
[0115] In an embodiment, the elongated castellation elements 25A
extending longitudinally between the shelves or counter discs 14 on
the sidewall 81 of the grinding element 80 can be arranged follow a
helical path about the axial direction 6 of the mill shell.
[0116] In other embodiments, any other alternative longitudinal
shapes of the elongated castellation elements 25A may be
utilized.
[0117] In an embodiment, the elongated castellation elements 25A
extending longitudinally between the shelves or counter discs 14 on
the sidewall 81 of the grinding element 80 only traverse a portion
of the distance between the shelves or counter discs 14.
[0118] In an embodiment, the elongated castellation elements 25A
extending longitudinally between the shelves or counter discs 14 on
the sidewall 81 of the grinding element 80 may each comprise two or
more castellation element segments cascaded in line or in other
pattern. The castellation element segments may be block-shaped
segments, or pole-shaped segments, or they may have any other
shape, such as hexagonal, oval or any other polygonal shape,
depending on an application.
[0119] In embodiments, the castellation elements 25A and 25B may
have holes, interruptions or cut outs in order to allow sludge
circulation around the castellation elements.
[0120] In embodiments of the invention, a grinding element 80 may
have a cage-like structure with axial support structure which
comprises a plurality of elongated spaced support members 25A
defining the outer periphery of the grinding element 80, and at
least one counter disc 14 is connected to and arranged to project
radially inward from the plurality of elongated spaced support
members 25A of the axial support structure, as illustrated in the
example shown in FIG. 12. In the example of FIG. 13, the grinding
element 80 has a cross-section of a hollow half-cylinder with three
annular castellated shelves or counter discs 14. The exemplary
grinding element 80 may be similar to a stack of three grinding
elements 80 of FIG. 8, except that the sidewall 81 is omitted. In
other words, the members 25A of axial support structure are
interconnected by the shelves 14 so that a cage-like structure is
obtained. Similarly, a cage-like grinding element 80 can be
achieved from other embodiments disclosed above by omitting the
sidewall 81. Otherwise, various embodiments and features described
above are applicable also in embodiments having a cage-like
structure. The elongated spaced support members 25A may also act as
castellation for the shell 18 of the mill body. A cage-like
grinding element 80 does not protect the shell 18 as well as a
grinding element 80 having a sidewall 81, but it is lighter in
weight, easier to handle, and has lower manufacturing cost.
[0121] Referring to FIG. 14, in yet another embodiment, one or more
of the castellation elements 25A and 25B may act as a skeleton for
coating with a dissimilar material 40. The coating of the
dissimilar material 40 may be arranged to form a sacrificial
protective layer over the castellation elements 25A and 25B and the
inner surface of the sidewall 81. The sacrificial protective
material 40 may be used for providing more easily replaceable
integrated grinding elements 80, as the material 40 may make the
grinding element 80 more rigid. This may be particularly useful in
embodiments having a cage-like structure. The sacrificial
protective material 40 may also prolong the service life of the
castellation elements 25A and 25B and the sidewall 81, although it
may be arranged to wear off within a very short period of time
after the installation and start of the grinding operation. The
dissimilar material may be polyurethane, for example. For example,
grinding element 80 with the castellation elements 25A and 25B
coated with or embedded in the sacrificial material 40 may appear
as having a flat inner surface at the time of installation and
obtain final shape during the operation after the sacrificial
material 40 has worn out.
[0122] While the embodiments have been described with reference to
a vertically arranged mill body and grinding mill, the invention
may also be used in other mill types, such as grinding mills having
a horizontally arranged or an angled mill body.
[0123] Furthermore, while the embodiments have been described with
reference to grinding mills of the type that use stationary mill
shells 18 or mill bodies 2 with rotating stirring shafts 11 and
stirring elements 12, embodiments of the invention are also
applicable to grinding mills of the type that use rotating mill
shells 18 or mill bodies 2 with stationary stirring shafts 11 and
stationary stirring elements 12 arranged in the grinding chamber
15. The rotating axis of the shell 18 or mill body 2 may be coaxial
with the mill body 2, or non-coaxial. The rotating axis may be
parallel to a longitudinal axis 6 of the mill body 2, or the
rotating axis may be inclined or at an angle to the axis of the
mill body.
[0124] Still further, embodiments of the invention are also
applicable to grinding mills of the type that use rotating mill
shells 18 or mill bodies 2 and rotating stirring shafts 11 and
stirring elements 12 arranged in the grinding chamber 15.
[0125] The rotating axis of the shell 18 or mill body 2 may be
coaxial with the rotating axis of the stirring shaft 11, or
non-coaxial. The rotating axis of the shell 18 or mill body 2 may
be parallel to the rotating axis of the stirring shaft 11, or the
rotating axis of the shell 18 or mill body 2 may be inclined or at
an angle to the rotating axis of the stirring shaft 11.
[0126] It will further be appreciated that any of the features in
the exemplary embodiments of the invention can be combined together
and are not necessarily applied in isolation from each other. For
example, different types of grinding elements 80 may be used in the
same mill shell. Some grinding element 80 may have the castellation
25A and/or 25B while other grinding elements 80 may be without the
castellation 25A and/or 25B. The shear forces and wear are
typically highest at the bottom part of the shell, and the
castellation 25A and/or 25B may thus preferably be provided at
least to the bottom part of the shell.
[0127] Similar combinations of two or more features from the above
described embodiments or preferred forms of the invention can be
readily made by one skilled in the art.
[0128] The grinding elements according to embodiments of the
invention may create a protective layer or zone of the grinding
media against the wearable components, the invention reduces the
amount of wear and thus prolongs the operational life of the
components of the grinding mill, reducing maintenance time, costs
and improving efficiency of the grinding mill. The protective layer
or zone generated by the castellation may also promotes slurry
particle contact with the grinding media, also improving grinding
efficiency. Thus, the grinding mill is able to operate more
efficiently, consuming components such as grinding discs at lower
rates while grinding at faster rates. Moreover, the can be readily
retrofitted in existing fine grinding mills. In all these respects,
the invention represents a practical and commercially significant
improvement over the prior art.
[0129] Although the invention has been described with reference to
specific examples, it will be appreciated by those skilled in the
art that the invention may be embodied in many other forms.
* * * * *